This invention relates to solid fuel pulverizing and firing systems for fossil fuel furnaces of the type, wherein the fossil fuel furnace and a substantial portion of the solid fuel pulverizing and firing system by means of which solid fuel and air is supplied to the fossil fuel furnace, are operated at a predetermined pressure, and more specifically, to an exhauster employable in such solid fuel pulverizing and firing systems for fossil fuel furnaces having an improved fan assembly.
Three basic types of solid fuel pulverizer firing systems find common use. These are the direct-fired system, the semi-direct fired system, and the bin storage system. The simplest and most commonly used of these three systems, and the one to which the present invention is directed, is the direct-fired system win which solid fuel, e.g., coal, is fed in a suitable manner along with hot gases to a pulverizer. The solid fuel is simultaneously ground and dried within the pulverizer. The drying of the solid fuel is effected by the hot gases as the latter sweep through the pulverizer. As the hot gases sweep through the pulverizer they are cooled and humidified by means of the evaporation of the moisture contained in the solid fuel. Often, an exhauster is employed for purposes of removing the hot gases and the entrained fine solid fuel particles, i.e., the solid fuel that has been ground within the pulverizer, from the pulverizer. Moreover, this exhauster, when so employed, is located on the discharge side of the pulverizer and is operative to effect the delivery of the mixture of hot gases and entrained fine solid fuel particles to a fossil fuel furnace. The main advantages of the direct-fired system are simplicity, low cost and maximum safety. To this end, the fine solid particles, which can be subject to spontaneous combustion and thus are considered to be potentially hazardous, go directly to the fossil fuel furnace at high velocities, and thus are not given the opportunity to collect and possibly ignite spontaneously. Accordingly, the direct-fired system can be operated at the maximum temperatures that safety will permit.
One prior art form of such a direct-fired solid fuel pulverizer firing system is depicted in U.S. Pat. No. 3,205,843 entitled "Pulverized Coal Firing System" in which it is disclosed that solid fuel passes through the inlet chute 23 of the pulverizer 26 on to the rotating bowl 32 thereof. The solid fuel thus admitted to the pulverizer 26 is pulverized therewithin by means of the grinding rollers 36 of the pulverizer 26, which are mounted within the pulverizer housing to provide a grinding action between the grinding rollers 36 and the grinding ring provided on the rotating bowl 32 of the pulverizer 26. Air passes up through the pulverizer 26 between the housing thereof and the rim of the rotating bowl 32 and as the air passes the rotating bowl 32, pulverized solid fuel is entrained in this air with the air-pulverized solid fuel mixture passing up into the classifier 40 of the pulverizer 26, which is located in the upper portion of the pulverizer 26. The classifier 40 is effective to separate the coarse solid fuel fractions and return these fractions to the rotating bowl 32 of the pulverizer for regrinding, while the fines retained in the air stream pass through the outlet 42 of the pulverizer 26, which is located at the upper end of the classifier 40. From this outlet 42 of the pulverizer 26, the air-pulverized solid fuel mixture is conveyed to the inlet of the exhauster 46 via conduit 44. The air-pulverized solid fuel mixture in turn is conveyed from the exhauster 46 to the fossil fuel furnace 10 through the ducts 48.
Another prior art form of an exhauster for a solid fuel pulverizer firing system is depicted in U.S. Pat. No. 5,363,776 to Wark entitled "Exhauster Inlet Venturi". The Wark '776 patent discloses a known pulverizer exhauster fan assembly 10 having a fan 18 with a plurality of radial fan blades 20 connected to a drive shaft 22 by a spider assembly 24. The drive shaft 22 ends in a hub 23 which is capped by a "cooley cap" radial diverter cap 26.
Although solid fuel pulverizer firing systems constructed in accordance with the teachings of the two issued U.S. patents to which reference has been made heretofore have been demonstrated to be operative for the purpose for which they have been designed, there has nevertheless been evidenced in the prior art a need for such solid fuel pulverizer firing systems to be further improved, and more specifically, a need for the exhauster employed therein to be improved. A limiting factor insofar as the operating efficiency of exhausters is concerned has heretofore been the need to facilitate maintenance particularly on the fan assembly thereof. The need for such maintenance is occasioned principally by the fact that the material which is transported through the exhauster is extremely abrasive. To this end, a need has thus been evidenced in the prior art for a new and improved solid fuel pulverizer firing system, and more specifically for a new and improved exhauster for such solid fuel pulverizer firing systems that would require relatively less maintenance than known exhausters.
Moreover, there has been evidenced in the prior art a need for such a new and improved exhauster for such solid fuel pulverizer firing systems that would further be characterized in a number of additional respects. One such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability of achieving therewith an even greater reduction in the amount of erosion to which certain interior surfaces of the exhauster. A further additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is that the exhauster would be capable of embodying all of the above-enumerated characteristics while yet retaining the existing casing of an exhauster.
It is, therefore, an object of the present invention to provide a new and improved exhauster for use in solid fuel pulverizer firing systems.
It is a further object of the present invention to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized by its reduced need for maintenance as compared to prior art forms of exhausters.
Yet another object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is possible therewith to achieve all of the foregoing within the existing casing of an exhauster.
Yet a further object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that use may be made thereof either in retrofit applications or in new applications.
Yet another further object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is relatively simple in construction, relatively easy to operate, yet is relatively inexpensive to provide.